iPhone 14 Pro: all calls fail in <20s

Hi all, I got a brand new iPhone 14 Pro 1Tb, non-US hardware (with a physical SIM card). I then left for a short trip to the USA, where I still am, and all calls fail between 10 and 20 seconds from starting, whether calling or receiving. I’m trying to understand if the device is defective or it’s a software issue. I guess that - if it wasn’t just me - it’d be in the news, like the rattling camera. Other kinds of calls, like using Signal, have no issues.

Can you suggest what to do to understand if I need to return the device to the shop? I’ve already reset the network settings. Thanks.

G.